The thrust of the post is that the council ordered the destruction of iconoclast books, aside from those held in a private collection by the patriarch of Constantinople. The existence of such a collection may explain some of the reading material listed by Photius in his Bibliotheca.
What I was not clear about, tho, was what the historical sources quoted were. How do we know this?
Sadly a firewall prevents me posting a comment, but if you know, please let me know.
I find that this is supposedly from the 9th canon of the canons of the council. In the NPNF translation these read:
That none of the books containing the heresy of the traducers of the Christians are to be hid.
All the childish devices and mad ravings which have been falsely written against the venerable images, must be delivered up to the Episcopium of Constantinople, that they may be locked away with other heretical books. And if anyone is found hiding such books, if he be a bishop or presbyter or deacon, let him be deposed; but if he be a monk or layman, let him be anathema.
Ancient Epitome of Canon IX.
If any one is found to have concealed a book written against the venerable images, if he is on the clergy list let him be deposed; if a layman or monk let him be cut off.
What here is styled Episcopium was the palace of the Patriarch. In this palace were the archives, and this was called the “Cartophylacium,” in which the charts and episcopal laws were laid up. To this there was a prefect, the grand Chartophylax, one of the principal officials and of most exalted dignity of the Church of Constantinople, whose office Codinus explains as follows: “The Ghartophylax has in his keeping all the charts which pertain to ecclesiastical law (that is to say the letters in which privileges and other rights of the Church are contained) and is the judge of all ecclesiastical causes, and presides over marriage controversies which are taken cognizance of, and proceedings for dissolution of the marriage bond; moreover, he is judge in other clerical strifes, as the right hand of the Patriarch.”
In this Cartophylaceum or Archives, therefore, under the faithful guardianship of the Chartophylax, the fathers willed that the writings of the Iconoclasts should be laid up, lest in their perusal simple Catholics might be led astray.
But here at IntraText I find a different version of the text. Now IntraText is not a scanning site; they just use what others upload. So which translation is this? The same text is here. I also find it here with attribution to Peter L’Huillier.
After much searching, I find online “Canons of the seven ecumenical councils from the Rudder trans. by D. Cummings, 1957, with intro by Archbishop Peter L’Huillier.” (Chicago: Orthodox Christian Educational Society) and discussed here.